# Angular Code Review Guide

> Angular 17+ 代码审查指南，覆盖 Signals、Standalone 组件、RxJS 反模式、Zoneless 变更检测、模板最佳实践及性能优化等核心主题。

## 目录

- [Signals 与变更检测](#signals-与变更检测)
- [Standalone 组件迁移](#standalone-组件迁移)
- [RxJS 反模式](#rxjs-反模式)
- [Zoneless 变更检测](#zoneless-变更检测)
- [模板最佳实践](#模板最佳实践)
- [性能优化](#性能优化)
- [测试](#测试)
- [路由守卫](#路由守卫)
- [依赖注入模式](#依赖注入模式)
- [HttpInterceptor](#httpinterceptor)
- [Review Checklist](#review-checklist)

---

## Signals 与变更检测

### Signal + OnPush 自动触发变更检测

```typescript
// ❌ 可变状态 + OnPush = 界面不更新
@Component({
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `<p>{{ data.name }}</p>`,
})
export class UserProfile {
  data = { name: 'Alice' };
  changeName() { this.data.name = 'Bob'; } // UI 不会更新！
}

// ✅ Signal + OnPush = 自动变更检测
@Component({
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `<p>{{ name() }}</p>`,
})
export class UserProfile {
  name = signal('Alice');
  changeName() { this.name.set('Bob'); } // 自动触发 CD
}
```

### @Input() 对象变异不会被 OnPush 检测

```typescript
// ❌ 变异 Input 对象——引用不变，OnPush 不检测
@Input() config!: Config;
updateConfig() { this.config.theme = 'dark'; }

// ✅ 创建新引用
updateConfig() { this.config = { ...this.config, theme: 'dark' }; }
```

### computed() 用于派生状态

```typescript
// ❌ effect 用于同步状态——反模式，可能触发额外 CD 周期
export class CartComponent {
  total = signal(0);
  discounted = signal(0);

  constructor() {
    effect(() => this.discounted.set(this.total() * 0.9));
  }
}

// ✅ computed 用于派生状态——惰性计算，无副作用
export class CartComponent {
  total = signal(0);
  discounted = computed(() => this.total() * 0.9);
}
```

### effect() 中 Signal 读取在 await 后不会被追踪

```typescript
// ❌ await 之后读取 Signal——依赖未被追踪
effect(async () => {
  const data = await fetchUserData();
  console.log(`Theme: ${theme()}`); // theme() 未被追踪！
});

// ✅ 在 await 之前同步读取
effect(async () => {
  const currentTheme = theme(); // 同步读取，被追踪
  const data = await fetchUserData();
  console.log(`Theme: ${currentTheme}`);
});
```

### effect 只在特定场景使用

```typescript
// ❌ 用 effect 同步两个 Signal——永远用 computed
effect(() => { this.filtered.set(this.items().filter(i => i.active)); });

// ✅ effect 的合理场景：DOM 操作、分析日志、订阅外部源
effect(() => {
  const canvas = this.canvasRef.nativeElement;
  const ctx = canvas.getContext('2d');
  ctx.fillStyle = this.color();
  ctx.fillRect(0, 0, this.size(), this.size());
});

// 💡 "There are no situations where effect is good,
//    only situations where it is appropriate."
```

---

## Standalone 组件迁移

### Angular 19+ standalone 是默认值

```typescript
// ❌ Legacy NgModule 组件
@Component({
  selector: 'old-component',
  standalone: false,
})
export class OldComponent {}

// ✅ 现代 Standalone 组件（Angular 19+ standalone 是默认值）
@Component({
  selector: 'user-profile',
  imports: [ProfilePhoto, RouterLink],
  template: `<profile-photo /><a routerLink="/edit">Edit</a>`,
})
export class UserProfile {}
```

### 审查标记

```typescript
// ⚠️ 需要迁移的信号：
// 1. standalone: false
// 2. @NgModule declarations
// 3. 组件通过 NgModule 而非直接 import

// ✅ 迁移路径：
// 1. 删除 standalone: false
// 2. 将依赖添加到组件的 imports 数组
// 3. 如果不再有 declarations，删除 NgModule
```

---

## RxJS 反模式

### subscribe() 必须配 takeUntilDestroyed

```typescript
// ❌ 裸 subscribe——内存泄漏！组件销毁后仍继续接收数据
@Component({ /* ... */ })
export class UserProfile implements OnInit {
  ngOnInit() {
    this.data$.subscribe(data => this.processData(data));
  }
}

// ✅ takeUntilDestroyed——自动在组件销毁时取消（需在构造函数或注入上下文中调用）
@Component({ /* ... */ })
export class UserProfile {
  constructor() {
    this.data$.pipe(takeUntilDestroyed()).subscribe(data => {
      this.processData(data);
    });
  }
}

// ✅ 在构造函数外使用——传入 DestroyRef
@Component({ /* ... */ })
export class UserProfile {
  private destroyRef = inject(DestroyRef);

  startListening() {
    this.data$.pipe(takeUntilDestroyed(this.destroyRef)).subscribe(/* ... */);
  }
}
```

### toSignal 优于 AsyncPipe

```typescript
// ❌ AsyncPipe——需要导入，模板中有 | async
@Component({
  imports: [AsyncPipe],
  template: `{{ data$ | async }}`,
})

// ✅ toSignal——自动取消订阅，可在任何地方使用
export class UserProfile {
  data = toSignal(this.data$, { initialValue: null });
  // 模板直接用 data()
}
```

### 避免重复 toSignal 调用

```typescript
// ❌ toSignal 每次调用都创建新订阅
getData() {
  return toSignal(this.http.get('/api/data'));
}

// ✅ 存储结果
data = toSignal(this.http.get('/api/data'), { initialValue: null });
```

---

## Zoneless 变更检测

### 普通属性变异不会被检测（Angular 21+）

```typescript
// ❌ Zoneless 下普通属性赋值不触发 CD
export class UserService {
  user: User | null = null;
  loadUser() { this.user = fetchResult; } // 不触发！
}

// ✅ Signal 自动触发 CD
export class UserService {
  private _user = signal<User | null>(null);
  readonly user = this._user.asReadonly();
  loadUser() { this._user.set(fetchResult); }
}
```

### NgZone API 在 Zoneless 中失效

```typescript
// ❌ NgZone.onStable 在 zoneless 中永远不会触发
ngZone.onStable.subscribe(() => { /* 永远不触发 */ });

// ✅ 使用 afterNextRender
afterNextRender({ write: () => { /* CD 之后执行 */ } });
```

### Reactive Forms 变异需要 markForCheck

```typescript
// ❌ Reactive Forms 的 setValue/patchValue 在 zoneless 中不自动调度 CD
this.form.patchValue({ name: 'Alice' }); // UI 可能不更新

// ✅ 手动标记或通过 Signal 反映
this.form.patchValue({ name: 'Alice' });
this.cdr.markForCheck();
```

### Zoneless 下有效的 CD 触发器

| 触发器 | 说明 |
|--------|------|
| `signal.set()` / `.update()` | Signal 更新自动触发 |
| `ChangeDetectorRef.markForCheck()` | 手动标记 |
| `ComponentRef.setInput()` | 输入绑定 |
| 模板事件监听器回调 | 用户交互 |

---

## 模板最佳实践

### 复杂逻辑提取为 computed Signal

```typescript
// ❌ 模板中复杂表达式
template: `<div *ngIf="items.filter(i => i.active).length > 0 && user.role === 'admin'">`

// ✅ 提取为 computed
filteredItems = computed(() => this.items().filter(i => i.active));
shouldShow = computed(() => this.filteredItems().length > 0 && this.user().role === 'admin');
template: `@if (shouldShow()) { <div>...</div> }`
```

### 原生绑定优于 NgClass / NgStyle

```typescript
// ❌ NgClass/NgStyle——额外指令开销
template: `<div [ngClass]="{active: isActive}" [ngStyle]="{'color': textColor}">`

// ✅ 原生 class/style 绑定——性能更好
template: `<div [class.active]="isActive" [style.color]="textColor">`
```

### 模板专用成员标记 protected

```typescript
// ❂ 模板专用方法暴露为 public
export class UserProfile {
  formatName(name: string) { return name.trim(); }
}

// ✅ 模板专用成员用 protected
export class UserProfile {
  protected formatName(name: string) { return name.trim(); }
}
```

### Angular 管理的属性标记 readonly

```typescript
// ❌ input/output/model 可被意外覆盖
userId = input<string>();
userSaved = output<void>();

// ✅ readonly 防止意外赋值
readonly userId = input<string>();
readonly userSaved = output<void>();
readonly userName = model<string>();
```

### 命名规范：操作名而非事件名

```typescript
// ❌ 以事件命名
template: `<button (click)="handleClick()">Save</button>`

// ✅ 以操作命名
template: `<button (click)="saveUserData()">Save</button>`
```

---

## 性能优化

### effect 是最后手段——优先 computed

```typescript
// ❌ effect 用于状态同步——触发额外 CD，可能无限循环
effect(() => {
  this.filteredItems.set(this.items().filter(i => i.active));
});

// ✅ computed——惰性计算，无副作用，无额外 CD
filteredItems = computed(() => this.items().filter(i => i.active));
```

### afterRenderEffect 分离读写阶段

```typescript
// ❌ 无阶段指定 = mixedReadWrite = 额外 DOM 回流
afterRenderEffect(() => {
  const height = el.offsetHeight; // 读
  el.style.height = height + 10 + 'px'; // 写
});

// ✅ 分离阶段减少回流
afterRenderEffect({
  earlyRead: () => el.offsetHeight,
  write: (height) => { el.style.height = height() + 10 + 'px'; },
  read: () => verifyLayout(),
});
```

### inject() 优于构造函数注入

```typescript
// ❌ 构造函数注入——多依赖时难以阅读
export class UserService {
  constructor(
    private http: HttpClient,
    private router: Router,
    private auth: AuthService,
  ) {}
}

// ✅ inject()——更好的类型推断和可读性
export class UserService {
  private http = inject(HttpClient);
  private router = inject(Router);
  private auth = inject(AuthService);
}
```

---

---

## 测试

### 组件测试（TestBed）

```typescript
// ✅ 独立组件测试
@Component({
  standalone: true,
  template: `<button (click)="increment()">{{ count() }}</button>`,
})
export class CounterComponent {
  count = signal(0);
  increment() { this.count.update(c => c + 1); }
}

describe('CounterComponent', () => {
  let fixture: ComponentFixture<CounterComponent>;

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      imports: [CounterComponent],
    }).compileComponents();

    fixture = TestBed.createComponent(CounterComponent);
    fixture.detectChanges();
  });

  it('should increment on click', () => {
    const button = fixture.nativeElement.querySelector('button');
    button.click();
    fixture.detectChanges();
    expect(button.textContent.trim()).toBe('1');
  });
});
```

### 服务测试（依赖注入 Mock）

```typescript
// ✅ 使用 TestBed.inject + provide 覆盖
@Injectable({ providedIn: 'root' })
export class UserService {
  private http = inject(HttpClient);
  getUser(id: number) {
    return this.http.get<User>(`/api/users/${id}`);
  }
}

describe('UserService', () => {
  let service: UserService;
  let httpMock: HttpTestingController;

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [provideHttpClient(), provideHttpClientTesting()],
    });
    service = TestBed.inject(UserService);
    httpMock = TestBed.inject(HttpTestingController);
  });

  afterEach(() => httpMock.verify());

  it('should fetch user', () => {
    const mockUser = { id: 1, name: 'Alice' };

    service.getUser(1).subscribe(user => {
      expect(user).toEqual(mockUser);
    });

    const req = httpMock.expectOne('/api/users/1');
    expect(req.request.method).toBe('GET');
    req.flush(mockUser);
  });
});
```

### 集成测试策略

```typescript
// ❌ 过度 Mock——测试的是 Mock 而非真实行为
provideHttpClient: () => ({
  get: jasmine.createSpy().and.returnValue(of(mockData)),
}),

// ✅ 使用 HttpTestingController 验证真实 HTTP 交互
TestBed.configureTestingModule({
  providers: [
    provideHttpClient(),
    provideHttpClientTesting(),
  ],
});

// ✅ 浅渲染：只测试组件本身，Mock 子组件
describe('UserProfile', () => {
  it('should pass user to child', () => {
    const fixture = TestBed.createComponent(UserProfile);
    fixture.componentRef.setInput('user', testUser);
    fixture.detectChanges();

    const child = fixture.debugElement.query(By.directive(UserAvatar));
    expect(child.componentInstance.user()).toEqual(testUser);
  });
});
```

---

## 路由守卫

### AuthGuard / CanActivate

```typescript
// ✅ 函数式路由守卫（Angular 15+ 推荐）
export const authGuard: CanActivateFn = (route, state) => {
  const auth = inject(AuthService);
  const router = inject(Router);

  if (auth.isAuthenticated()) return true;

  return router.createUrlTree(['/login'], {
    queryParams: { returnUrl: state.url },
  });
};

// 使用
export const routes: Routes = [
  {
    path: 'dashboard',
    component: DashboardComponent,
    canActivate: [authGuard],
  },
];
```

### 延迟加载路由守卫

```typescript
// ✅ 守卫在路由加载时才被解析
// auth.guard.ts
export const authGuard: CanActivateFn = () => {
  const auth = inject(AuthService);
  return auth.isAuthenticated();
};

// routes.ts
export const routes: Routes = [
  {
    path: 'admin',
    loadChildren: () => import('./admin/routes').then(m => m.routes),
    canActivate: [authGuard],
  },
];
```

### 参数化路由守卫

```typescript
// ✅ 带角色参数的守卫
export function roleGuard(allowedRoles: string[]): CanActivateFn {
  return (route, state) => {
    const auth = inject(AuthService);
    const user = auth.currentUser();
    return user ? allowedRoles.includes(user.role) : false;
  };
}

// 使用
{
  path: 'admin',
  component: AdminComponent,
  canActivate: [roleGuard(['admin', 'superadmin'])],
}
```

### CanDeactivate 守卫

```typescript
// ✅ 防止未保存修改的导航离开
export const unsavedChangesGuard: CanDeactivateFn<EditFormComponent> = (
  component
) => {
  if (component.hasUnsavedChanges()) {
    return confirm('You have unsaved changes. Leave anyway?');
  }
  return true;
};
```

---

## 依赖注入模式

### InjectionToken 使用

```typescript
// ❌ 使用字符串 token——易冲突且无类型安全
providers: [{ provide: 'API_URL', useValue: 'https://api.example.com' }]

// ✅ InjectionToken 提供类型安全
export const API_URL = new InjectionToken<string>('API_URL');

providers: [{ provide: API_URL, useValue: 'https://api.example.com' }]

// 使用
private apiUrl = inject(API_URL);
```

### 多级提供者

```typescript
// ✅ 不同注入层级
// 根级——全局单例
@Injectable({ providedIn: 'root' })
export class GlobalService {}

// 组件级——每个组件实例独立
@Component({
  providers: [LocalService],
})
export class MyComponent {
  private local = inject(LocalService);
}

// 路由级——路由及其子路由共享
{
  path: 'checkout',
  providers: [CheckoutService],
  children: [/* ... */],
}
```

### 工厂提供者

```typescript
// ✅ 根据条件动态提供不同实现
export const themeProvider: FactoryProvider = {
  provide: ThemeService,
  useFactory: () => {
    const platform = inject(PLATFORM_ID);
    if (isPlatformServer(platform)) {
      return new ServerThemeService();
    }
    return new BrowserThemeService();
  },
};

// ✅ 使用环境变量配置
export const apiConfigProvider: FactoryProvider = {
  provide: ApiConfig,
  useFactory: () => {
    const env = inject(ENVIRONMENT);
    return env.production
      ? new ProductionApiConfig()
      : new DevelopmentApiConfig();
  },
};
```

---

## HttpInterceptor

### 认证 Token 拦截器

```typescript
// ✅ 函数式拦截器——自动附加 Auth Token
export function authInterceptor(
  req: HttpRequest<unknown>,
  next: HttpHandlerFn
): Observable<HttpEvent<unknown>> {
  const token = inject(AuthService).token();
  if (!token) return next(req);

  return next(req.clone({
    setHeaders: { Authorization: `Bearer ${token}` },
  }));
}

// 注册
provideHttpClient(withInterceptors([authInterceptor]))
```

### 错误处理拦截器

```typescript
// ✅ 函数式拦截器——统一错误处理
export function errorInterceptor(
  req: HttpRequest<unknown>,
  next: HttpHandlerFn
): Observable<HttpEvent<unknown>> {
  const router = inject(Router);

  return next(req).pipe(
    catchError((error: HttpErrorResponse) => {
      if (error.status === 401) {
        router.navigate(['/login']);
      }
      if (error.status === 500) {
        console.error('Server error:', error);
      }
      return throwError(() => error);
    })
  );
}
```

### 请求/响应转换

```typescript
// ✅ 函数式拦截器——自动 camelCase ↔ snake_case
export function transformInterceptor(
  req: HttpRequest<unknown>,
  next: HttpHandlerFn
): Observable<HttpEvent<unknown>> {
  const transformedBody = req.body ? toSnakeCase(req.body) : null;
  const transformedReq = req.clone({ body: transformedBody });

  return next(transformedReq).pipe(
    map(event => {
      if (event instanceof HttpResponse) {
        return event.clone({ body: toCamelCase(event.body) });
      }
      return event;
    })
  );
}
```

### 拦截器顺序

```typescript
// ✅ 拦截器按注册顺序执行
// 请求：A → B → C → 后端
// 响应：后端 → C → B → A
provideHttpClient(
  withInterceptors([
    authInterceptor,
    loggingInterceptor,
    errorInterceptor,
  ])
)
```

## Review Checklist

### Signals 与变更检测

- [ ] Signal + OnPush 用于模板状态（非可变对象）
- [ ] `@Input()` 对象通过新引用更新（非变异）
- [ ] 派生状态用 `computed()`，不用 `effect()`
- [ ] `effect()` 中 Signal 读取在 `await` 之前
- [ ] `effect()` 只用于 DOM 操作、日志、外部源订阅

### Standalone 组件

- [ ] 无 `standalone: false`（Angular 19+）
- [ ] 组件通过 `imports` 数组导入依赖
- [ ] 无不必要的 `@NgModule`

### RxJS

- [ ] `.subscribe()` 配 `takeUntilDestroyed` 或 `async` pipe
- [ ] 优先 `toSignal` 而非 `AsyncPipe`
- [ ] 无重复 `toSignal` 调用

### Zoneless

- [ ] 模板状态通过 Signal 管理（非普通属性）
- [ ] 无 `NgZone.onStable` / `NgZone.onMicrotaskEmpty`
- [ ] Reactive Forms 变异后有 `markForCheck()`

### 模板

- [ ] 复杂逻辑提取为 `computed` Signal
- [ ] 使用原生 `[class]`/`[style]` 而非 `NgClass`/`NgStyle`
- [ ] 模板专用成员标记 `protected`
- [ ] `input`/`output`/`model` 属性标记 `readonly`
- [ ] 事件处理器以操作命名（`saveData` 而非 `handleClick`）

### 性能

- [ ] `effect()` 不用于状态同步
- [ ] `afterRenderEffect` 分离读写阶段
- [ ] `inject()` 用于依赖注入